1. Field of the Invention
The present invention relates to measurement of input and output levels of base station transmitters in a mobile communication system and more particularly to an apparatus for measuring input and output levels of base station transmitters in the mobile communication system, for allowing measurement of an input/output level of a transmitting stage so as to check an operation state of a digital block through detection of an intermediate frequency (IF) output level of the transmitting stage and an operation state of a transmitter by the frequency allocation (FA) through measurement of an output level of the transmitter.
2. Description of Related Art
Generally, a mobile communication system such as a CDMA mobile communication system or a digital cellular system performs forward (from base station to mobile station) power control and reverse (from mobile station to base station) power control.
Particularly, the CDMA mobile communication system uses the forward and reverse power control to obtain advantages such as large traffic carrying capacity and calls of good quality.
Mobile station transmission power is controlled to ensure that a base station receiver receives transmission signals of all mobile stations within a service area at a nominal strength.
Mobile station transmission signals are designed to be received with the same strength regardless of the mobile station""s location and propagation loss. When the transmission power of all the mobile stations within the service area is controlled in such manner, total received power of the base station receiver can be calculated in such a manner of multiplying the nominal received power by the number of mobile stations.
It is very important to measure the state of a base station transmitter in optimally controlling the base station transmission power. This is because the transmission power cannot be properly controlled without knowing the base station transmission power.
FIG. 1 shows a configuration of an embodiment of a distribution and combine shelf unit (DICSU that is a component making up the transmitting stage) within the base station of the conventional mobile communication system when 4FAs are applied.
Attenuation block 1 includes first to fourth attenuators 1axcx9c1d for attenuating four transmission IF signals, TXxe2x80x94IF, of 4.95MHz as much as desired. 4:5 switch 2 switches the IF signals output from the first to fourth attenuators 1axcx9c1d in the attenuation block 1. Transmitter block 3 up-converts the IF signals received from the 4:5 switch 2 to provide radio frequency (RF) signals.
Attenuation and amplification block 4 includes first to fifth attenuator-amplifiers 4axcx9c4e for attenuating and amplifying the RF signals received from respective transmitters in the transmitter block 3 down to a predetermined level and up to a predetermined level to provide outputs. Isolator block 5 includes first to fifth isolators 5axcx9c5e for preventing transmission errors caused by reflected waves of the RF signals output from the attenuator-amplifiers in the attenuation and amplification block 4. RF combiner 6 combines the RF signals from the respective isolators 5axcx9c5e in the isolator block 5 to forward a single transmitting RF signal.
Once four transmitting IF signals, TX_IF, of 4.95MHz modulated in the CDMA mode are input into such DICSU within the conventional mobile communication base station, the first to fourth attenuators 1axcx9c1d in the attenuation block 1 respectively attenuate the four IF signals down to 5 dB before sending them to the 4:5 switch 2.
The 4:5 switch 2 switches the input signals to the transmitter block 3 including four transmitters 3axcx9c3d respectively coupled to 4FAs and one spare transmitter 3e. 
The 4:5 switch 2 just couples the four input IF signals to the corresponding first to fourth transmitters 3axcx9c3d when the first to fourth transmitters 3axcx9c3d in the following transmitter block 3 operate in normal. In this case, the fifth transmitter 3e does not have an input signal. When a certain transmitter among the first to fourth transmitters 3axcx9c3d is in an abnormal state, the 4:5 switch cuts off the first erroneous transmitter and switches the IF signal that is expected to be input into the erroneous transmitter to the fifth transmitter 3e. 
The first to fifth transmitters 3axcx9c3e in the transmitter block 3 up-convert the input IF signals into RF signals before sending them to the attenuation and amplification block 4.
The first to fifth attenuator-amplifiers 4axcx9c4e in the attenuation and amplification block 4 attenuate the input RF signals and amplify the attenuated RF signals up to a predetermined level before sending them to the isolator block 5.
The first to fifth isolators 5axcx9c5e in the isolator block 5 compensate signals output from the first to fifth attenuator-amplifiers 4axcx9c4e and provide the compensated RF signals to the RF combiner 6. The RF combiner 6 combines the RF signals input through different paths to output a transmitting signal via one output port.
However, in the conventional base station DICSU, input signals are just transmitted to the transmitter and combined at the combiner to provide an output. The conventional DICSU does not have a function of checking errors that may occur in transmission paths.
In the conventional art, an operator should manually search for erroneous parts with test equipment when some errors occur in the transmission paths. This is very inconvenient.
Moreover, it takes too much time to find out erroneous parts.
Since the error check function is not provided, the operator cannot be informed of output levels of transmitters and levels of the CDMA modulated input signals.
When the gain of a transmitter drops, a present switching condition of the transmitter should be changed. However, the conventional switch changes the switching state only when failing in setting channels due to failure in transmitter""s PLL locking. The conventional switch without a function of detecting the gain of a transmitter cannot change the present switching condition with respect to the transmitter having the dropped gain.
Accordingly, the present invention is directed to an apparatus for measuring input and output levels of base station transmitters in the mobile communication system that substantially obviates one or more of the limitations and disadvantages of the related art.
An objective of the present invention is to provide an apparatus for measuring input and output levels of base station transmitters in the mobile communication system, for allowing measurement of an input/output level of a transmitting stage so as to check an operation state of a digital block through detection of an intermediate frequency (IF) output level of the transmitting stage and an operation state of a transmitter by the frequency allocation (FA) through measurement of an output level of the transmitter.
Additional features and advantages of the invention will be set forth in the following description, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure as illustrated in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, in a base station signal distribution and combine shelf unit (DICSU) including a switch for switching IF to be transmitted via transmitters to a plurality of transmitters, a plurality of amplifiers for amplifying a plurality of transmitter output signals, and a radio frequency (RF) combiner for receiving a plurality of amplifier output signals via a plurality of isolators and combining a plurality of RF signals to forward a combined signal through a single path, an apparatus comprises: a frequency splitting block disposed prior to the switch, for splitting the IF to be transmitted via the transmitters; a frequency selection block for selecting and outputting one of a plurality of signals output from the frequency splitting block according to a transmitter selection signal output from a central processing unit that controls overall system operation; an amplification and filtering block for amplifying an output signal from the frequency selection block up to a predetermined level and filtering an amplified signal to provide a signal of a set band; a coupler for providing a signal corresponding to the signal output from the RF combiner as a transmitter output level signal; a phase locked loop block for generating oscillation frequency of a predetermined band according to control of the central processing unit; a frequency mix and filtering block for amplifying the signal output from the coupler up to a predetermined level, mixing the amplified signal with the signal output from the phase locked loop block, and band filtering a mixed signal to provide an output; an output level detection block for detecting a level of the signal output from the frequency mix and filtering block; the central processing unit for applying the selection signal for a transmitter to be measured to the frequency selection block so as to select the transmitter, storing the signals respectively output from the amplification and filtering block and the frequency mix and filtering block in an internal memory as input and output levels of the selected transmitter, and providing the transmitter input and output level values stored in the internal memory to an RF control card assembly; and the RF control card assembly for controlling switch of the transmitter based upon the transmitter input and output level values received from the central processing unit.
The frequency selection block consists of a multiplexer that selects one of the plurality of signals output from the frequency splitting block according to the transmitter selection signal output from the central processing unit for controlling the overall system operation.
The amplification and filtering block comprises: an amplifier for amplifying the signal output from the frequency selection block; an attenuator for attenuating a signal output from the amplifier; and a band filter for filtering an output signal from the attenuator to provide a signal having the set band.
The frequency mix and filtering block comprises: an amplifier for amplifying the signal output from the coupler up to the predetermined level; an attenuator for attenuating an output signal from the amplifier down to a predetermined level; a frequency mixer for mixing output frequency from the attenuator with the oscillation frequency output from the phase locked loop block; and a band filter for filtering output frequency from the frequency mixer to obtain the signal of the set band.
The apparatus for measuring input and output levels of base station transmitters according to the present invention further comprises: a first voltage amplification block for operational-amplifying the output signal from the amplification and filtering block and providing an amplified signal to the central processing unit; and a second voltage amplification block for operational-amplifying the output signal from the output level detection block and providing an amplified signal to the central processing unit.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.